1. Field of the Invention
The present invention relates generally to a surface cleaning apparatus and method using plasma, and in particular, to a surface cleaning apparatus and method for, using plasma, removing a native oxide layer resulting from reaction between oxygen in the air and a silicon, silicide or metal surface in fabrication of an integrated circuit such as semiconductor device or TFT (Thin Film Transistor) LCD (Liquid Crystal Display), an oxide layer chemically formed on the silicon surface during processing, a damaged portion on the silicon surface, or contaminants on the silicon surface and the sidewalls of a contact hole.
2. Description of the Related Art
In general, metalization is needed to connect devices formed on an underlying silicon substrate by a metal layer in fabrication of an integrated circuit such as a semiconductor, TFT LCD, or FPD (Flat Panel Display). Formation of a contact hole is requisite for the metalization. The contact hole is formed usually by dry-etching an oxide layer using plasma. In the course of forming the contact hole, the underlying silicon, silicide or metal surface is exposed. After the dry etch, a damaged portion is formed due to ion impact from the plasma, and contaminants including materials dissociated from etching gases and etched materials stick to a silicon surface and sidewalls. Because the damaged portion and contaminants may increase contact resistance or leakage current that is deadly adverse to device characteristics, they are removed by dry cleaning or wet cleaning during fabrication of an integrated circuit. Aside from the damaged portion and contaminants, a native oxide layer is formed due to reaction between oxygen in the air and the silicon, silicide or metal surface. Therefore, the native oxide layer should also be removed by dry cleaning or wet cleaning before deposition of a conductive material after the contact hole is formed.
In addition, an oxide layer can be chemically formed by reaction between the silicon surface and a mixed solution of H2O2, H2SO4, and deionized water used for post-etch processing. The oxide layer influences subsequent steps and deteriorates electrical connection characteristics, thereby degrading the characteristics of a resulting semiconductor or TFT LCD circuit.
Along with the decrease of CD(Critical Dimension) in an integrated circuit, a self-aligned contact (SAC) has recently been used widely. During an SAC etch, an etch stopper layer made of a silicon nitride layer is exposed. Thus, either sidewalls formed of a silicon oxide layer or the nitride layer should not be etched during surface cleaning in order to prevent short between an electrode surrounded by the nitride film and a conductive material filling the contact hole as well as minimizing leakage current.
Even if the silicon substrate surface underlying the contact hole is not closed, a gate, a polysilicon electrode for a capacitor, or a connection line can be exposed. In this case, a damaged portion, an oxide layer, or contaminants should be removed as in the case where the silicon substrate surface is exposed.
A metal is used for a gate electrode or bit lines of a memory when necessary. The top portion of the metal is exposed during etching a contact hole. Similarly, contaminants on the metal and sidewalls must be removed and much attention should be paid to the removal because etched metal components are contained in the contaminants and are difficult to remove.
FIG. 1 is a schematic view of a conventional fluorine acid spray apparatus. Referring to FIG. 1, the conventional fluorine acid spray apparatus is comprised of a fluorine acid solution 10, a heating chamber 20, a substrate 30, a substrate mount 40, a fluorine solution tank 50 filled with a fluorine acid solution 60, and fluorine acid supply pipes 70 and 80. To prevent formation of a native oxide layer, oxygen is preliminarily removed by forming a fluorine layer on a silicon surface to react with the oxygen. Specifically, a fluorine acid layer is formed on a silicon surface by generating fluorine acid vapor using the fluorine acid spray apparatus and hardened by heat. Oxygen introduced into an etching device to etch the fluorine acid layer-having substrate or oxygen remaining in the etching device reacts chemically with the fluorine acid layer on the surface of the substrate and thus the oxygen is removed.
Despite the advantage of simplicity in device configuration and concept, however, the above conventional technology has a shortcoming in that it is difficult to effectively control fine process parameters.
UV (UltraViolet) light and ozone (O3) can be used for surface cleaning. That is, a silicon surface is oxidized by reaction between silicon and O3 dissociated by UV light and the oxide layer is removed by wet etch. However, oxidation takes a long time, leading to slow processing accurately.
FIG. 2 is a schematic view of a conventional plasma etching apparatus. plasma is generated in a plasma generator 100 by introducing H2 and N2 through a first processing gas inlet 90 and then NF3 is introduced through a second processing gas inlet 110, thereby etching a silicon substrate 120 in a chamber 140 with gases exhausted through an outlet 130.
The NF3 gas as a main processing gas accelerates plasma dissociation and activation, so that excess fluorine atoms and ions involved in the etching are generated. As a result, the silicon surface is over-etched deeper than a damaged portion, or a BPSG (Borophosphosilicate glass) oxide layer or a nitride layer that must avoid etching may also be etched. This is due to a a low selection ratio between native oxide etch rate and etch rate of silicon, BPSG or nitride when NF3 is used.
Another feature in which an inert gas such as Ar as a first processing gas shows a slow etch rate.
Therefore, it is required to provide improved cleaning method other than a conventional wet or dry etching method as described above.